This invention relates to a process of making an ink jet image display, more particularly to process of making an ink jet image display using a recording element which contains adhesive particles.
In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An ink jet recording element typically comprises a support having on at least one surface thereof a base layer for absorbing fluid and an ink-receiving or image-forming layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
It is often desirable to bond an ink jet image via the front surface, i.e., the ink-receiving surface, onto another substrate to form a final bonded composite. Such imaged and bonded composites find utility in a variety of image display applications. For example, an inkjet image could be printed on a transparent support and mounted onto a rigid opaque substrate to provide a rigid composite for direct viewing through the transparent support. An ink jet image could also be printed onto a light-diffusing opaque polyester support with a transparent polyester film laminated to its surface to provide a composite for a backlit display.
U.S. Pat. No. 5,795,425 discloses an ink jet imaging element wherein an ink jet image is deposited onto an adhesive receptor layer which is coated onto a protective layer and a temporary carrier layer. After imaging, the temporary carrier layer is peeled away. However, there is a problem with this element, however, in that it requires a temporary carrier layer and the adhesive receptor layer is not porous so that it has a longer dry time.
U.S. Pat. No. 4,785,313 discloses a recording element comprising a support having thereon an ink transporting layer and an ink retaining layer. The ink transporting layer may contain non-dyeable particles in a binder which is required to be non-dyeable. However, there is a problem with this element in that the dye image has to go through an ink transporting layer until it reaches the ink retaining layer, thus causing the image to spread which reduces image quality.
It is an object of this invention to provide a process of making an ink jet image display using an ink jet recording element which can be laminated to another support for image display applications and which has superior adhesion. It is another object of this invention to provide a process of making an ink jet image display using an ink jet recording element which when printed with an ink jet image will have a fast dry time.
This and other objects are provided by the present invention comprising a process for making an ink jet image display comprising:
A) providing an ink jet recording element comprising a substantially transparent support having thereon, in the order recited, a base layer comprising a hydrophilic or porous material and a porous, ink-receptive top layer capable of accepting an ink jet image comprising a polymeric adhesive binder and thermally-activated adhesive polymeric particles, the particle-to-binder ratio being between about 95:5 and 70:30, and wherein both the binder and the polymer used to make the polymeric particles have:
a) a tensile strength at break of greater than about 1 MPa;
b) an elongation at break of greater than about 10%;
c) a tensile modulus of greater than about 1 MPa; and
d) a Tg of less than about 50xc2x0 C.;
and the polymeric particles also having a particle size of less than about 10 xcexcm and a Tm or softening point of greater than about 50xc2x0 C.;
B) printing an ink jet image on the recording element;
C) bringing the top layer of the recording element in contact with another substrate to form a composite assemblage; and
D) subjecting the composite assemblage to heat and pressure to adhere the recording element to the substrate to form the ink jet image display.
In a preferred embodiment of the invention, both the polymeric binder and the polymer used to make the adhesive polymeric particles used in the recording element for the process of the invention have:
a) a tensile strength at break of between about 1 MPa and about 70 MPa, preferably between about 2 MPa and about 50 MPa;
b) an elongation at break between about 10% and about 2,000%, preferably between about 100% and about 1,000%;
c) a tensile modulus of between about 1 MPa and about 500 MPa, preferably between about 2 MPa and about 400 MPa; and
d) a Tg of less than about 50xc2x0 C., preferably from about xe2x88x9260xc2x0 C. to about 20xc2x0 C.
In order for the ink-receptive top layer to be sufficiently porous, the particle-to-binder ratio should preferably be between about 95:5 and 70:30, preferably between about 90:10 and 80:20. If the particle-to-binder ratio is above the range stated, the layer will not have any cohesive strength. If the particle-to-binder ratio is below the range stated, the layer will not be porous enough to provide a fast dry time.
The polymer used to make the thermally-activated adhesive, polymeric particles used in the invention may be a partially crystalline or an amorphous polymer, for example, a polycaprolactone such as Tone(copyright) (Union Carbide Corp.), an ethylene-vinyl acetate copolymer such as Elvax(copyright) (DuPont Corp.), a styrene-ethylene/butylene-styrene block copolymer such as Kraton(copyright) (Shell Chemical Corp.), a polyamide such as Griltex CoPolyamide(copyright) (EMS American Grilon Corp.), or a polyester such as Griltex CoPolyester(copyright) (EMS American Grilon Corp.). Other suitable materials can be found in the Handbook of Common Polymers CRC Press 1971, and Properties of Polymers Elsevier 1990. In a preferred embodiment, the polymer used to make the polymeric particles comprises a polycaprolactone.
The thermally-activated adhesive, polymeric particles used in the invention may be made using various techniques, such as, for example, evaporative limited coalescence as described in U.S. Pat. No. 4,833,060. Other techniques may also be used such as limited coalescence as described in U.S. Pat. No. 5,354,799, or cryogenic grinding as described in U.S. Pat. No. 4,273,294.
As noted above, the polymer used to make the thermally-activated adhesive polymeric particles has a melting temperature, TM, of greater than about 50xc2x0 C., or a softening point of greater than about 50xc2x0 C. The Tm is measured using a differential scanning calorimeter (DSC). In a preferred embodiment, the Tm is between about 60xc2x0 C. and 120xc2x0 C. A softening point of a polymer can be measured by the Ring and Ball method as described in ASTM E28.
The polymeric adhesive binder useful in the top layer of the recording element used in the invention may be, for example, a polyurethane such as a Witcobond(copyright) Aqueous Urethane Dispersion (Witco Corp.), a vinyl acetate-ethylene copolymer emulsion, an ethylene-vinyl chloride copolymer emulsion, a vinyl acetate-vinyl chloride-ethylene terpolymer emulsion such as Airflex(copyright) (Air Products Corp.), an acrylic emulsion such as Flexbond(copyright) (Air Products Corp), or polyvinyl alcohol such as Airvol(copyright) (Air Products Corp). In a preferred embodiment, the adhesive binder comprises a polyurethane.
The base layer, in general, has a thickness of about 1 xcexcm to about 20 xcexcm and the top layer will usually have a thickness of about 2 xcexcm to about 50 xcexcm.
The base layer is primarily intended to act as a sponge layer for the absorption of ink solvent. As such, it is primarily composed of hydrophilic or porous materials. Generally, the base layer is present in an amount from about 5 g/m2 to about 7 g/m2, preferably from about 5.3 g/m2 to about 5.5 g/m2. Suitable hydrophilic materials include gelatin, acetylated gelatin, phthalated gelatin, oxidized gelatin, chitosan, poly(alkylene oxide), poly(vinyl alcohol), modified poly(vinyl alcohol), sulfonated polyester, partially hydrolyzed poly(vinylacetate/ vinyl alcohol), poly(acrylic acid), poly(1-vinylpyrrolidone), poly(sodium styrene sulfonate), poly(2-acrylamido-2-methane sulfonic acid), polyacrylamide or mixtures thereof. Copolymers of these polymers with hydrophobic monomers may also be used. Suitable porous materials for a base layer include, for example, silica or alumina in a polymeric binder, including hydrophilic binders such as those described above.
In a preferred embodiment of the invention, the base layer comprises gelatin which may have up to about 15% of another hydrophilic material such as poly(1-vinylpyrrolidone).
As stated above, the support of the recording element used in the invention is substantially transparent. Examples of such supports include various plastics including a polyester-type resin such as poly(ethylene terephthalate), polycarbonate resins, polysulfone resins, methacrylic resins, cellophane, acetate plastics, cellulose diacetate, cellulose triacetate, vinyl chloride resins, poly(ethylene naphthalate), polyester diacetate, and various glass materials. The thickness of the support employed in the invention can be, for example, from about 12 to about 500 xcexcm, preferably from about 75 to about 300 xcexcm. In a preferred embodiment, the support is a substantially transparent poly(ethylene terephthalate) film.
If desired, in order to improve the adhesion of the base layer to the support, the surface of the support may be corona-discharge-treated prior to applying the base layer or solvent-absorbing layer to the support. Alternatively, an under-coating, such as a layer formed from a halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl acetate copolymer can be applied to the surface of the support.
Since the image recording element may come in contact with other image recording articles or the drive or transport mechanisms of image recording devices, additives such as surfactants, lubricants, matte particles and the like may be added to the element to the extent that they do not degrade the properties of interest. In addition, the top layer of the recording element used in the process of the invention may also contain other additives such as viscosity modifiers or mordants.
The layers described above, including the base layer and the top layer, may be coated by conventional coating means onto a support material commonly used in this art. Coating methods may include, but are not limited to, wound wire rod coating, slot coating, slide hopper coating, gravure, curtain coating and the like. Some of these methods allow for simultaneous coatings of both layers, which is preferred from a manufacturing economic perspective.
As noted above, the composite assemblage is subjected to heat and pressure to adhere the recording element to another substrate to form the ink jet image display. This may be done, for example, by passing the assemblage through a pair of heated rollers at temperatures of, for example, from about 90xc2x0 C. to about 180xc2x0 C. at a pressure of from about 0.05 to about 5 MPa.
The other substrate to which the recording element described above may be adhered can be virtually any substrate which is desired to be used, either flexible or rigid, opaque or transparent. In a preferred embodiment, the substrate is rigid and opaque, such as FomeCor(copyright) Graphic-Arts Board (International Paper Co.).
Ink jet inks used to image the recording elements employed in the present invention are well-known in the art. The ink compositions used in ink jet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. The dyes used in such compositions are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, U.S. Pat. Nos. 4,381,946; 4,239,543 and 4,781,758, the disclosures of which are hereby incorporated by reference.